arXiv subjects

Youngsub Yoon

Publications and source records attributed to Youngsub Yoon.

At least 19 recordsLinked to original sources

arXiv2026

Revisiting Data Quality Control and Multiple-star Modeling in Wide Binary Gravity Tests: Confirmation of MOND-type Gravitational Anomaly at Low Acceleration

Wide binary stars provide natural laboratories for directly probing gravity in the low-acceleration regime, as dark matter inferred from any viable gravity has negligible effects on their internal dynamics. Various recent studies including Bayesian 3D analyses have shown that wide binaries with separations greater than several thousand astronomical units experience MOND-type gravity with a boost factor of $\gamma\approx 1.3-1.6$. However, results claiming preference for, or no deviation from, standard gravity have also been published during the same period, particularly highlighting the roles of data quality control and realistic modeling of multiple-star (i.e., triple and higher-order) systems that host hidden companion stars. Here we carefully reexamine the issues of data quality control and modeling multiple-star systems in statistical gravity tests based on sky-projected 2D velocities of wide binary stars. Through extensive tests including the acceleration-plane test, the $\tilde v$-distribution test, and the median-$\tilde v$-profile test (where $\tilde v$ is the sky-plane 2D relative velocity normalized by the Newtonian circular velocity between the two stars), we show that proper data quality control or reasonable variation in multiple-star modeling cannot remove the low-acceleration gravitational anomaly but confirms the MOND-type gravitational anomaly, particularly consistent with recent realistic MOND solutions of wide binary orbits. We find that studies claiming no evidence for the low-acceleration gravitational anomaly are consequences of bypassed calibration of the fraction of multiple-star systems using the Newtonian-regime data, bias-introduction in data quality control that is not taken into account in gravity tests, or insufficient statistics in the low-acceleration regime.

astro-ph.GA↗

arXiv2026

Comparison of MOND and Verlinde's emergent gravity in dwarf spheroidals

We apply Modified Newtonian Dynamics (MOND) and Verlinde's emergent gravity separately to calculate the radial accelerations in 23 dwarf spheroidals. Then, we compare them with the observed radial accelerations. In our earlier work, we determined that, when the data set is considered in its entirety without isolating individual dwarf spheroidal, Verlinde's emergent gravity is in close agreement with the observed values. In the present work, we additionally confirm that, for 21 of the 23 samples examined, Verlinde's emergent gravity follows the trend of the observed values within each dwarf spheroidal more closely than MOND. Combining the statistical significance of all the 23 samples, ranging from $-0.25\sigma$ to 3.41$\sigma$, we conclude that Verlinde's emergent gravity is favored over MOND at 5.2$\sigma$.

gr-qc↗

arXiv2025

Probing the nature of gravity in the low-acceleration limit: wide binaries of extreme separations with perspective effects

Recent statistical analyses of wide binaries have revealed a boost in gravitational acceleration with respect to the prediction by Newtonian gravity at low internal accelerations $\lesssim 10^{-9}$ m\,s$^{-2}$. This phenomenon is important because it does not permit the dark matter interpretation, unlike galaxy rotation curves. We extend previous analyses by increasing the maximum sky-projected separation from 30 to 50 kilo astronomical units (kau). We show that the so-called ``perspective effects'' are not negligible at this extended separation and, thus, incorporate it in our analysis. With wide binaries selected with very stringent criteria, we find that the gravitational acceleration boost factor, $\gamma_g \equiv g_{\rm obs}/g_{\mathrm N}$, is $1.61^{+0.37}_{-0.29}$ (from $\delta_{\rm obs-newt}\equiv (\log_{10}\gamma_g)/\sqrt{2}=0.147\pm0.062$) at Newtonian accelerations $g_{\mathrm N} = 10^{-11.0}$ m\,s$^{-2}$, corresponding to separations of tens of kau for solar-mass binaries. At Newtonian accelerations $g_{\mathrm N} = 10^{-10.3}$ m\,s$^{-2}$, we find $\gamma_g=1.26^{+0.12}_{-0.10}$ ($\delta_{\rm obs-newt}=0.072\pm0.027$). For all binaries with $g_{\rm N}\lesssim10^{-10}$ m\,$s^{-2}$ from our sample, we find $\gamma_g=1.32^{+0.12}_{-0.11}$ ($\delta_{\rm obs-newt}=0.085\pm0.027$). These results are consistent with the generic prediction of MOND-type modified gravity, although the current data are not sufficient to pin down the low-acceleration limiting behavior. Finally, we emphasize that the observed deviation from Newtonian gravity cannot be explained by the perspective effects or any separation-dependent eccentricity variation which we have taken into account.

astro-ph.GA↗

arXiv2024

Understanding the Radial Acceleration Relation of Dwarf Galaxies with Emergent Gravity

We examine whether the radial acceleration relation (RAR) of dwarf galaxies can be explained by Verlinde's emergent gravity. This is the extension of arXiv:2206.11685v3, which examines the RAR of typical spiral galaxies, to less massive systems. To do this, we compile the line-of-sight velocity dispersion profiles of 30 dwarf galaxies in the Local Group from the literature. We then calculate the expected gravitational acceleration from the stellar component in the framework of the emergent gravity, and compare it with that from observations. The calculated acceleration with the emergent gravity under the assumption of a quasi-de Sitter universe agrees with the observed one within the uncertainty. Our results suggest that the emergent gravity can explain the kinematics of galaxies without introducing dark matter, even for less massive galaxies where dark matter is expected to dominate. This sharply contrasts with MOND, where a new interpolating function has to be introduced for dwarf galaxies to explain their kinematics without dark matter.

gr-qc↗

arXiv2023

New method to revisit the gravitational lensing analysis of the Bullet Cluster using radio waves

Gravitational lensing studies of the Bullet Cluster suggested convincingly in favor of the existence of dark matter. However, it was performed without the knowledge of the original orientation of each galaxy before gravitational lensing. A potential improvement to this issue lies in the measurement of the original orientation from the polarization direction of radio waves emitted from each galaxy. In this context, Francfort et al. derived a formula that can utilize the information about the original orientation of each galaxy to obtain what is called {\it shear}. However, we demonstrate that shear in their formula should be replaced by {\it reduced shear} when the change in sizes of images of galaxies is taken into account. As the previous gravitational lensing analysis of the Bullet Cluster used reduced shear, we suggest applying our improved formula directly for the reanalysis once we obtain the polarization direction of radio waves. In particular, we show that our new formula can yield a more accurate analysis than the previous one, if the polarization direction can be measured more precisely than $10^\circ$. Moreover, the approach discussed in this work is generically applicable to the gravitational lensing analysis of clusters, not only limited to the Bullet Cluster.

astro-ph.CO↗

arXiv2023

Inflation and the late time acceleration from Hossenfelder-Verlinde gravity

We show that Hossenfelder's covariant formulation of Verlinde's emergent gravity predicts inflation and the late-time acceleration at the same time, without assuming a separate field such as inflaton, whose sole purpose is producing inflation. In particular, for the current deceleration parameter $q=-0.95$ to $-0.55$, we obtained $\lambda^2$, the mass of the imposter field, from $1.85\times 10^4$ to $2.26\times 10^4$. We also note that the value of $\lambda$ around $q=-0.93$ coincides with the inverse of fine structure constant.

gr-qc↗

arXiv2022

Understanding Galaxy Rotation Curves with Verlinde's Emergent Gravity

We present the results from the analysis of galaxy rotation curves with Verlinde's emergent gravity. We use the data in the SPARC (Spitzer Photometry and Accurate Rotation Curves) database, which contains a sample of 175 nearby disk galaxies with 3.6 $\mu$m surface photometry and rotation curves. We compute the gravitational acceleration at different galactocentric radii expected from the baryon distribution of the galaxies with the emergent gravity, and compare it with the observed gravitational acceleration derived from galactic rotation curves. The predicted and observed accelerations agree well with a mean offset $\mu{\rm [log(g_{obs})-log(g_{Ver})]}=-0.060\pm0.004$ and a scatter $\sigma{\rm [log(g_{obs})-log(g_{Ver})]}=0.137\pm0.004$ by assuming a de Sitter universe. These offset and scatter become smaller when we assume a more realistic universe, quasi de Sitter universe, as $\mu=-0.027\pm0.003$ and $\sigma=0.129\pm0.003$. Our results suggest that Verlinde's emergent gravity could be a good solution to the missing mass problem without introducing dark matter.

gr-qc↗

arXiv2020

Verlinde gravity effects on the orbits of the planets and the Moon in the Solar System

In this work, we address the effects of a phenomenon known as Verlinde gravity. Here we show that its effect over the planets and the Moon in our solar system is quite negligible. We find that the Verlinde gravity effects on the orbits of planets are at least 10 times smaller than the precision with which we can determine the Sun's mass, and the one on the orbit of the Moon is about 100 times smaller than the precision with which we can determine the Earth's mass. These results let us infer that statements in the literature that Verlinde gravity is ruled out by the observed motion of planets in our solar system aren't correct.

gr-qc↗

arXiv2020

Comment on "Inconsistencies in Verlinde's emergent gravity"

In 2016, Erik Verlinde proposed a new theory of gravity called "emergent gravity" by using mathematical formulas used in the theory of elasticity. In 2017, De-Chang Dai and Dejan Stojkovic claimed to point out inconsistencies in Verlinde's emergent gravity. We point out that their claim was based on misunderstanding of the dictionary between emergent gravity and theory of elasticity. In addition, we propose a slightly different formula for Verlinde's emergent gravity.

gr-qc↗

arXiv2019

Comment on "Emergent Gravity and the Dark Universe" by Erik Verlinde

Verlinde suggested a new theory of gravity called ``emergent gravity,'' which resembles Modified Newtonian Dynamics, the alternative to dark matter theory. For his version of Milgrom's constant, he theoretically derived $a_M=cH_0/6=1.1\times 10^{-10}$m/s$^2$ by assuming that our universe is a flat de Sitter space, which is not certainly true. In 2022, when Park and us applied Verlinde's emergent gravity to galaxy rotation curves, we discovered that a slightly smaller value of $a_M$ is preferred. We re-ran our codes and obtained that a value about 30\% smaller than Verlinde's original value of Milgrom's constant is most preferred. This agrees with the value obtained recently by applying Verlinde's emergent gravity to the general FLRW universe.

physics.gen-ph↗

arXiv2018

CMB anisotropy power spectrum of 3-sphere universe for low $l$

We calculate the CMB anisotropy power spectrum of a closed universe for large angle (i.e., low $l$) due to a scale invariant fluctuation of primordial universe by considering the spherical harmonics for 3-sphere. In particular, contrary to the wide belief, we show that this consideration affects the CMB anisotropy power spectrum; instead of constant $l(l+1)C_l$, our consideration results in the supression for $l=2$, currently explained by the cosmic variance. As a more concrete proof of our analysis, from the low $l$ CMB anisotropy data \emph{alone}, we obtained $\Omega_{\mathrm{tot}}=1.0018^{+0.0031}_{-0.0007}$, which agrees with $\Omega_{\mathrm{tot}}=1.0023^{+ 0.0056}_{- 0.0054}$ from the previous anlaysis of WMAP+BAO+$H_0$. Thus, we conclude that our Universe is closed.

gr-qc↗

arXiv2017

Maxwell-Boltzmann type Hawking radiation

Twenty years ago, Rovelli proposed that the degeneracy of black hole (i.e. the exponential of the Bekenstein-Hawking entropy) is given by the number of ways the black hole horizon area can be expressed as a sum of unit areas. However, when counting the sum, one should treat the area quanta on the black hole horizon as distinguishable. This distinguishability of area quanta is noted in Rovelli's paper. Building on this idea, we derive that the Hawking radiation spectrum is not given by Planck radiation spectrum (i.e., Bose-Einstein distribution) but given by Maxwell-Boltzmann distribution.

gr-qc↗

arXiv2016

String coupling constant seems to be 1

We present a reasoning that the string coupling constant should be 1 from the assumption that the area spectrum derived from loop quantum gravity must be equal to the area spectrum calculated from "stringy differential geometry." To this end, we will use the loop quantum gravity area spectrum constructions proposed by Brian Kong and us, and stringy differential geometry based on double field theory recently proposed by Imtak Jeon, Kanghoon Lee and Jeong-Hyuck Park.

physics.gen-ph↗

arXiv2013

Problems with Mannheim's conformal gravity program

We show that Mannheim's conformal gravity program, whose potential has a term proportional to $1/r$ and another term proportional to $r$, does not reduce to Newtonian gravity at short distances, unless one assumes undesirable singularities of the mass density of the proton. Therefore, despite the claim that it successfully explains galaxy rotation curves, unless one assumes the singularities, it seems to be falsified by numerous Cavendish-type experiments performed at laboratories on Earth whose work have not found any deviations from Newton's theory. Moreover, it can be shown that as long as the total mass of the proton is positive, Mannheim's conformal gravity program leads to negative linear potential, which is problematic from the point of view of fitting galaxy rotation curves, which necessarily requires positive linear potential.

gr-qc↗

arXiv2012

Approximation of the naive black hole degeneracy

In 1996, Rovelli suggested a connection between black hole entropy and the area spectrum. Using this formalism and a theorem we prove in this paper, we briefly show the procedure to calculate the quantum corrections to the Bekenstein-Hawking entropy. One can do this by two steps. First, one can calculate the "naive" black hole degeneracy without the projection constraint (in case of the U(1) symmetry reduced framework) or the SU(2) invariant subspace constraint (in case of the fully SU(2) framework). Second, then one can impose the projection constraint or the SU(2) invariant subspace constraint, obtaining logarithmic corrections to the Bekenstein-Hawking entropy. In this paper, we focus on the first step and show that we obtain infinite relations between the area spectrum and the naive black hole degeneracy. Promoting the naive black hole degeneracy into its approximation, we obtain the full solution to the infinite relations.

gr-qc↗

arXiv2012

Quantum corrections to the Hawking radiation spectrum

In 1995, Bekenstein and Mukhanov suggested that the Hawking radiation spectrum was discrete if the area spectrum was quantized in such a way that the allowed areas were integer multiples of a single unit area. However, in 1996, Barreira, Carfora, and Rovelli argued that the Hawking radiation spectrum was continuous if the area spectrum was quantized with an infinite number of unit areas, as predicted by loop quantum gravity, rather than quantized with the single unit area considered by Bekenstein and Mukhanov. In this paper, contrary to what Barreira, Carfora, and Rovelli argued, we show that the Hawking radiation spectrum is still discrete when the area spectrum is quantized as loop quantum gravity predicts. In particular, we show that, for a black hole of a given temperature, the Hawking radiation spectrum is truncated at frequencies below a certain frequency.

gr-qc↗

arXiv2010

Black Hole Entropy Prediction without Immirzi Parameter

In our earlier paper "Corrections to the Bekenstein-Hawking entropy and the Hawking radiation spectrum", arXiv:0910.2755, we provided two concrete numerical evidences for the new area spectrum based on the Einstein-Kaufman pseudo tensor as opposed to the Ashtekar variables: namely, the reproduction of the Bekenstein-Hawking entropy without fixing Immirzi parameter and the reproduction of the Hawking radiation spectrum. In this article, we provide another concrete, numerical evidence for this new area spectrum; there was a constant in our earlier article, which was inversely proportional to the density of state, and which we could not fix a priori. Nevertheless, in our earlier article, we obtained this constant to be around 172~173 by fitting it to the Planck radiation spectrum. In this article, we calculate this value using another method. We obtain 172.87...which implies consistency.

physics.gen-ph↗

arXiv2009

Third potential evidence for the new area spectrum based on the Einstein-Kaufman pseudo tensor, a conjecture

This paper has been withdrawn by the authors. In our earlier paper "Corrections to the Bekenstein-Hawking entropy and the Hawking radiation spectrum", arXiv:0910.2755, we provided two concrete numerical evidences for the new area spectrum based on the Einstein-Kaufman pseudo tensor as opposed to the Ashtekar variables: namely, the reproduction of the Bekenstein-Hawking entropy without fixing Immirzi parameter and the reproduction of the Hawking radiation spectrum. In this article, we provide another potential, albeit not concrete, numerical evidence for this new area spectrum; there was a constant in our earlier article, which was inversely proportional to the density of state, and which we could not fix a priori. Nevertheless, in our earlier article, we obtained this constant to be around 172$\sim$173 by fitting it to the Planck radiation spectrum. In this article, we propose a mathematical formula that reproduces this value. According to this formula, this constant is around 172.8. Nevertheless, we failed to concretely derive this mathematical formula. Therefore, it is a conjecture.

physics.gen-ph↗